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Antiviral activity of dehydroascorbic acid.

Antiviral activity of vitamin C has been reported repeatedly over the years; however, the mechanism by which this activity occurs remains unknown. This lack of knowledge has led to speculation, and has resulted in unsatisfactory conclusions. Antiviral activity is commonly attributed simply to antioxidant properties, or even a more general "boosting of the immune system." These are vague, incomplete hypotheses, and recent research is providing much greater insight into vitamin C and the mechanism behind its observed antiviral effects.

In 2008, Furuya published research demonstrating that the oxidized form of vitamin C, dehydroascorbic acid (DHAA), has much stronger antiviral activity in vitro than ascorbic acid (AA).1 Furuya et al. tested three viruses of broadly different families; namely, herpes simplex virus type 1 (HSV-1), influenza virus type A, and poliovirus type 1. Their data show that both the herpes and influenza viruses were dramatically more sensitive to DHAA than AA alone. In further characterizing the antiviral effects, two mechanisms were proposed: one involving direct binding of DHAA, and the other increased radical production in the presence of AA.

One of the results reported by Furuya was puzzling, however. In an experiment to confirm the DHAA hypothesis, a solution in which iron was used to catalyze the conversion of AA to DHAA was contrasted with a solution prepared using commercially available, powdered DHAA. The catalytically prepared solution was expected to produce an amount of DHAA approximately equivalent to the amount present in the solution prepared from the commercial DHAA; thus the two solutions would be expected to have similar antiviral potency. Interestingly, this was not the case. Instead, the catalytically prepared solution demonstrated much stronger antiviral activity than the solution prepared with commercial DHAA. Furuya attributed the stronger effect of the AA + iron solution to the possibility of a prooxidant, cytotoxic effect. Although this remains a possibility, there is a much simpler, alternate explanation that was not mentioned and of which Furuya was possibly not aware. Commercially prepared, powdered DHAA is a dimer. Very recently Wechtersbach demonstrated that the dimeric form, when dissolved in pure water (as in the Furuya experiment), produces a solution that contains substantial proportions of various DHAA dimers in addition to the naturally occurring monomer.2 Thus it contains a considerably lower concentration of the monomer than would be expected based on the weighed-in amount. Dimer production would not be expected in the catalytically prepared solution.

It is conceivable, therefore, that Furuya's AA + iron solution actually contained a substantially higher concentration of the naturally occurring monomer than the solution prepared from the powdered DHAA. If that is true, it would argue even more strongly in favor of the DHAA binding hypothesis, and in the antiviral activity of natural DHAA.

Notes

(1.) Furuya A, Uozaki M, Yamasaki H, Arakawa T, Arita M, Koyama H. Antiviral properties of ascorbic and dehydroascorbic acid in vitro. Int I Mol Med. 2008;22:541-545.

(2.) Wechtersbach L et al. Stability and transformation of products formed from dimeric dehydroascorbic acid at low pH. FoodChem. 2011; doi:10.1016/j. foodchem,20ll.05.055.

Douglas Kitt, BS, MT(ASCP)

ReCverin LLC

3137 S. 330 W.

Salt Lake City, Utah 84115

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Author:Kitt, Douglas
Publication:Townsend Letter
Article Type:Report
Geographic Code:1USA
Date:Oct 1, 2011
Words:529
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